Laser energy can be transmitted through multiple optical fibers housed in a relatively flexible tubular catheter inserted into a body lumen, such as a blood vessel, ureter, fallopian tube, cerebral artery and the like to remove obstructions in the lumen. Catheters used for laser angioplasty and other procedures can have a central passage or tube which receives a guide wire inserted into the body lumen (e.g., vascular system) prior to catheter introduction. The guide wire facilitates the advancement and placement of the catheter to the selected portion(s) of the body lumen for laser ablation of tissue.
In designing a laser catheter, there are a number of considerations.
For example, laser energy should be controllably and selectively delivered onto single fibers or smaller sub-bundles of subsets of fibers that make up the total number of fibers that are incorporated into the device. This can reduce the overall impact of heat or acoustic shock that can damage tissue adjacent to the treatment site by dividing the transmitted laser energy into smaller packets. It can enable selective treating and targeting of specific zones encountered by the distal tip of the catheter by activating only the fibers required to heat those zones. It can reduce the overall power and energy requirements of the treatment laser by activating smaller portions of fibers in the catheter rather than activating all of the fibers simultaneously. When the instantaneous energy delivered by laser angioplasty catheters is maintained below an “adverse effect” threshold, while at the same time delivering the proper fluence values for tissue ablation, a significant reduction in the incidence of undesirable tissue damage can occur. Previous laser catheters able to energize controllably and selectively fibers used fairly complex scan systems including galvanometer scanners (open and closed loop), piezo type deflection devices, and other mechanical beam or coupler deflection systems. These types of systems typically require a fairly complex and expensive drive and control system. Often, diseased tissue is present in locations where only a portion of the laser catheter's distal tip is in contact with the diseased tissue. It may be desirable to activate only the portion of the distal tip in contact with the diseased tissue. Additionally, laser catheters are used to cut or ablate adhesions holding implanted objects in biological tissue. For safety reasons, it may be desirable to ablate only the tissue in contact with the laser delivery device tip and to avoid ablating tissue adjacent to the wall or artery to prevent perforation.
Notwithstanding these considerations, laser catheters typically energize all of the fibers simultaneously to achieve bulk ablation. Such fiber activation outputs energy from all fibers simultaneously. The resultant instantaneous energy required to achieve the fluence, or energy density values for ablation, can become high enough to induce undesirable tissue damage, including laser induced dissection.